Do not enable remote Bazel cache unless access key is present

This happens on PRs where the access key secret is not available for
security resasons. We can revert this once we have the cache public
again, but for now let's at least not fail PR builds.

Author: p0deje

.github/actions/cache-bazel/action.yml

@@ -50,10 +50,10 @@ runs:
     - run: |
         echo '${{ inputs.gcs-key }}' >> gcs.json
         echo "build --remote_cache=https://storage.googleapis.com/seleniumhq-bazel-remote-cache --remote_upload_local_results=${{ github.ref == 'refs/heads/trunk' }} --google_credentials=gcs.json" >> .bazelrc
-      if: runner.os != 'Windows'
+      if: inputs.gcs-key != '' && runner.os != 'Windows'
       shell: bash
     - run: |
         echo ${{ inputs.gcs-key }}>>gcs.json
         echo "build --remote_cache=https://storage.googleapis.com/seleniumhq-bazel-remote-cache --remote_upload_local_results=${{ github.ref == 'refs/heads/trunk' }} --google_credentials=gcs.json">>.bazelrc
-      if: github.ref == 'refs/heads/trunk' && runner.os == 'Windows'
+      if: inputs.gcs-key != '' && runner.os == 'Windows'
       shell: cmd